The present invention relates to heat resistant stainless steel wire and/or heat resistant stainless steel strip for an electric heater as used in a preheating plug for a Diesel engine, and particularly to heat resistant stainless steel wire and/or heat resistant stainless steel strip in which the bonding forces of a covering layer relative to substrate steel wire are strong.
Methods for applying a ceramic-metal composite covering to the surface of a based material or a substrate metal so far known include a Chemical Vapor Deposition (CVD) method, a Physical Vapor Deposition (PVD) method, a Solgel method, a flame coating and the like.
However, in the CVD method, materials for substrate metal and a covering matter are restricted, and in the PVD method, the bonding force of adhesion force between substrate metal and a covering matter is weak. Further, also in the Solgel method, the bonding force or adhesion force between the substrate metal and the covering matter is weak, and it is difficult to form a thick covering layer whose thickness exceeds 1 micron. Particularly, it is necessary to form fine rugged portions on the surface of substrate metal by the shot blast or the like before bonding the covering matter. It is therefore very difficult to form a covering layer on metal parts such as a thin wire, a thin sheet, small articles, etc.
Japanese Patent Application Laid-Open No. 287407/1993 discloses an example in which alloy powder such as nickel alloy, cobalt alloy, etc. is placed in firm contact with the surface of ceramic powder such as relatively coarse silicon nitride, alumina, etc. as ceramic based powder for metallurgy for covering the surface of substrate metal such as a machining tool. However, such substrate metals are insufficient in mechanical strength, and uses thereof are limited.
On the other hand, a stainless steel covered with aluminum by melt plating to enhance heat resistant ability has been heretofore put to practical use. However, in a stainless steel thin wire and a stainless steel sheet covered with aluminum by melt plating, an aluminum alloy layer obtained by melt plating is brittle, and stainless steel as a substrate metal becomes brittle at a high temperature. Likewise, an aluminum alloy layer obtained by diffusion treatment is also brittle, and the alloy layer is peeled off from the stainless steel wire as a based material or a substrate metal at a high temperature, and the substrate metal also becomes brittle.